Here's what the study says: At a 4 percent withdrawal rate, a portfolio stands a 25 percent chance of running out of money before 30 years elapses if it is composed entirely of bonds. Ironically, the risk-averse looking for safety in bonds may discover these investments to be stranglers.

A portfolio with a 4 percent annual withdrawal rate and a 16 percent allocation to stocks has a 10 percent chance of running out of assets prematurely. A 40 percent to 60 percent stock allocation is optimal, reducing the probability of running out of money to 6 percent.

That study also shows how using other rates of withdrawal can make or break a portfolio, given various stock/bond allocations. I encourage you to read it. It's definitely a page-turner that just might keep you up nights.

Mutual funds that send you monthly checks
To address baby boomers' need for help with retirement income, a couple of mutual fund firms have come to the rescue. They're offering funds that generate stable income streams using varying strategies.

Fidelity Income Replacement funds, which are composed of several Fidelity funds, are designed to pay out regular income streams intended to last for a specific number of years. Currently they sport dates ranging from 2016 to 2036 in two-year intervals.

So if you buy Fidelity Income Replacement 2016 fund, you'll get about 11.15 percent of the fund's assets paid out to you each year until 2016, at which point the fund's assets will be depleted. Fidelity Income Replacement 2036 fund initially generates annual payments of about 5.09 percent, and these payouts, if all goes according to plan, will increase to keep pace with inflation until 2036, when the money is scheduled to run out. The annual expense ratios of these funds range from 0.54 percent to 0.65 percent.

Is the income amount guaranteed? No. If the asset allocation strategy doesn't work out right, you might wind up with less. The payouts are expected to keep pace with inflation, and the payment amounts are expected to increase as the fund approaches its horizon date, but there are no guarantees.

Insurance annuity products come with guarantees and they also generally come with higher price tags and give you less control over your assets. You can access your money in the Fidelity funds at whim.

Vanguard recently announced plans to launch three funds that are designed to generate regular payments, too. As is the case with the Fidelity funds, they use a funds-of-funds approach. Vanguard Managed Payout Growth Focus, Managed Payout Growth and Distribution, and Managed Payout Distribution Focus will annually distribute 3 percent, 5 percent and 7 percent, respectively. But rather than deplete assets by a set target date, these funds are designed to preserve capital at the same time. Their estimated annual expense ratio is expected to range from 0.57 to 0.58 percent -- higher than its original estimate of 0.34 percent.

Again, there are no guarantees. The payouts are adjusted each year, based on fund performance over the previous three years.

We all know by now that life offers few guarantees. Nevertheless, these funds provide boomers with more options as we confront the most difficult financial challenge yet. It's something we have to get right, lest we live out our own personal horror stories.

Longtime financial journalist Barbara Mlotek Whelehan earned a certificate of specialization in financial planning. If you have a comment or suggestion about this column, write to Boomer Bucks.